This invention relates to electroless plating operations and, in particular, to a method of determining the suitability of materials for electroless plating operations.
Electroless copper plating is a significant step in the fabrication of printed circuit boards. Unfortunately, some of the components of the bath or other materials which may be inserted in the bath, such as solder masks or photoresists, may introduce contaminants. If such a contamination effect is present, it may not be detected until a plating cycle is completed, which may be several hours and result in the destruction of many circuit boards. It is desirable, therefore, to test a material before it is inserted into a factory electroless bath to determine beforehand if it is suitable for the bath.
It has been proposed to use linear sweep voltammetry to measure the ratio of anodic and cathodic reaction rates of an electroless copper plating bath, and thereby determine if the copper deposited by the bath will pass certain stress tests. (See U.S. Pat. No. 4,908,242 issued to Hughes et al.) It has also been proposed to test for contaminants in electroless baths by superimposing an AC voltage on the standard DC voltage of a voltammetric apparatus, and then sweeping the DC voltage to provide characteristic AC current spectra for a bath and comparing that spectra with the AC spectra of a known acceptable bath. (See U.S. Pat. No. 4,631,116 issued to Ludwig.) It has further been suggested to use cyclic voltammetry to determine a Pd--Sn colloid peak and compare that value to a reference in order to determine if the activity of the colloid is sufficient for subsequent electroless plating. (See U.S. Pat. No. 4,820,643 issued to Amelio et al.)